The present invention relates to a method of making nanostructured metal-oxides using sol-gel chemistry, particularly to using metal salt precursors.
A new synthesis approach to forming energetic materials, specifically pyrotechnics, explosives, and propellants, using the chemical sol-gel methodology is described and claimed in U.S. application Ser. No. 08/926,357 filed Sep. 9,1997 and now U.S. Pat. No. 6,666,935, entitled “Sol-Gel Manufactured Energetic Materials” and in International Application No. PCT/US98/18262 (WO 99/12870) published Mar. 18, 1999. In energetic composites we can control oxidizer-fuel balances at the nanometer scale.
Sol-gel chemistry involves the reactions of chemicals in solution to produce nanometer-sized primary particles, called “sols.” The “sols” can be linked to form a three-dimensional solid network, called a “gel,” with the remaining solution residing within open pores. Solution chemistry determines the resulting nanostructure and composition, which in turn determine the material properties. Controlled evaporation of the liquid phase results in a dense porous solid, “xerogel.” Supercritical extraction (SCE) eliminates the surface tension and in so doing the capillary forces of the retreating liquid phase that collapse the pores. The results of SCE are highly porous, lightweight solids called “aerogels.” A typical gel structure is characteristically very uniform because the particles and the pores between them are on the nanometer size scale. Such homogeneity ensures uniformity of the material properties, which is one of the key reasons for synthesizing energetic materials using the sol-gel methodology.
Nanocomposites are multicomponent materials in which at least one of the component phases has one or more dimensions (length, width, or thickness) in the nanometer size range, usually defined as 1 to 100 nm. Energetic nanocomposites are a class of materials that have a fuel component and an oxidizer component intimately mixed in which at least one of the component phases which meets the size definition. A sol-gel derived pyrotechnic is an example of an energetic nanocomposite, in which metal-oxide nanoparticles react with metals and other fuels in very exothermic reactions. The fuel resides within the pores of the solid matrix while the oxidizer comprises at least a portion of the skeletal matrix. Nanometer to millimeter size materials can be added to the matrix and processed to form a xerogel to achieve the desired performance properties. The sol-gel formulations, reported here, allow for intimate mixing of components at the nanoscale level and again have the potential for water processing. This sol-gel methodology can be used to make nanostructured energetic materials with potentially superior performance than existing formulations, and incorporate all the safety and low toxicity considerations of water or other environmentally acceptable processing solvent-based systems.
The present invention is a new general synthetic route for producing nanostructured metal-oxides which employs the use of stable and inexpensive metal salts and environmentally friendly solvents such as water and ethanol in which the salts are dissolved, followed by the addition of a proton scavenger which induces gelation, after which the gel is dried to form an aerogel or a xerogel. Also, insoluble metals and polymers can be added just prior to gelation for changing the characteristics of the material. By this method many metal-oxide nanostructured materials have been synthesized using numerous metal salts. The invention of making metal-oxide-based materials using sol-gel chemistry is applicable to oxides formed from the following elements of the periodic table: Groups 2 through 13, part of Group 14 (germanium, tin, lead), part of Group 15 (antimony, bismuth), part of Group 16 (polonium), and the lanthanides and actinides.